This invention relates generally to cable television (CATV) communication systems. More particularly, the invention relates to a protocol for monitoring congestion on a CATV system and adjusting the power levels of communications between the settop terminals and the headend.
Over the last two decades, the availability of CATV service to individual homes has increased dramatically. A number of different types of CATV communication systems have evolved to provide a broader array of CATV services. Older “one-way” CATV systems primarily provide video programming services which are sent over the CATV physical link in a downstream direction from the headend of CATV system to a plurality of subscriber units.
Bidirectional CATV systems have become increasingly standard in the industry as the popularity and diversity of services has grown. These services may include but are not limited to pay-per-view, interactive banking, home shopping and Internet access. Bidirectional CATV systems support both downstream and upstream communications. Accordingly, individual subscribers may communicate with the headend, other subscribers or service providers within the system. These systems also permit subscribers to select specific video programming or consumer services and pay only for those services which are used. Some of these services, because of their interactive nature, require real-time communication paths between the subscriber units and servers in a headend. Digital cable networks are well suited for such applications. These networks consist of a cable plant which can be viewed as a point-to-multipoint environment, with the point being a headend and the multipoints being individual subscriber units. The coaxial or fiberoptic cable in the plant is considered to be a shared media. Data sent in the upstream direction travels from each subscriber unit toward the headend, while data sent in a downstream direction travels from the headend to the subscriber units.
Typically, a media access control (MAC) layer protocol is utilized to specify how the subscriber units communicate with the headend. A first problem exists in that multiple subscriber units may be simultaneously attempting to send data within the same upstream bandwidth towards the headend, thus causing upstream congestion. A second problem exists because each of the multiple subscriber units is positioned at a different location in the network. Therefore, when the headend is viewed from each of the multiple points, a different cable distance as well as a different number of line amplifiers and taps, and consequently a different attenuation will be experienced by the communications from a given subscriber unit to the headend. Since it is necessary to keep line amplifiers from saturating or letting signals go below the noise floor, upstream power levels should be adjusted for each subscriber unit.